Homes in the U.K. capital have been among the hottest global assets in recent years, but signs continue to suggest the heat is escaping.

Shares in Foxtons Group , a prominent London real-estate agent, plummeted 19% Thursday as it warned its full-year earnings will miss investors’ expectations, with a cooling London market cited as the culprit. Its third-quarter performance “was negatively impacted by a sharp and recent slowing of volumes in London property sales markets following an exceptionally strong nine-month period,” the firm said in a statement.

London has been the focus of a heated national debate on rapidly rising house prices. The Bank of England earlier this month asked the U.K. government for powerful new tools to curb real estate lending across the country, after the bank’s governor, Mark Carney, in June called the entire housing market “the greatest risk to the domestic economy.”

The most recent national statistics show London house prices were up nearly 20% on the year in July.

But over the summer, evidence mounted that a tipping point had been reached in London. Leading real-estate agents in September warned that constrained lending, looming interest rate rises, and political uncertainty were making buyers more cautious.

So far, market prices in high-end neighborhoods—targeted by international investors drawn to the U.K.’s robust property laws, stable currency, and a comparatively simple buying process for overseas capital—have been hardest hit. Last week, data from buying agency Huntly Hooper showed average sale prices for central London homes costing at least £10 million ($16.1 million) fell 7.4% on the year.

Foxtons expects the market “to continue to be constrained for some time due to political and economic uncertainty within the U.K. and Europe, tighter mortgage lending markets, and mismatches between the price expectations of buyers and sellers.”